Methods and apparatus for tuning in an inductive system

ABSTRACT

Electronic circuitry supports utilization of a series of pulses of varying width to tune a transducer (e.g., a coil that produces or receives a magnetic field) for transmitting or receiving. For example, a control voltage generator generates a sequence of digital pulses of varying pulse widths to produce respective control voltages. The control voltage generator applies a produced control voltage to a varactor element whose capacitance changes depending on a magnitude of the produced control voltage. The varactor element forms part of a tank circuit. Consequently, the series of pulse widths controls an operating frequency of the tank circuit at different times. The tank circuit includes an inductive coil that is tuned to produce or receive a magnetic or inductive field.

RELATED APPLICATIONS

This application is a Continuation of earlier filed U.S. patentapplication Ser. No. 10/978,515 entitled “METHODS AND APPARATUS FORTUNING IN AN INDUCTIVE SYSTEM,” (Attorney Docket No. AUR04-03, filed onNov. 1, 2004); which itself is a Continuation-In-Part (CIP) of earlierfiled U.S. patent application Ser. No. 10/004,989 entitled “WirelessCommunication Over a Transducer Device,” (Attorney Docket No.3058.1008-004, filed on Dec. 3, 2001); which itself is aContinuation-In-Part (CIP) earlier filed U.S. patent application Ser.No. 09/942,372 entitled “Wireless Communication Over a TransducerDevice,” (Attorney Docket No. 3058.1008-001), filed on Aug. 29, 2001;both of which claim the benefit of earlier filed U.S. Provisional PatentApplication Ser. No. 60/296,229 entitled “System and Method for WirelessCommunication,” (Attorney Docket No. 3058.1008-000), filed on Jun. 6,2001, and earlier filed U.S. Provisional Patent Application Ser. No.60/276,398 entitled “Techniques for a Wireless Communication System,”(Attorney Docket No. 3058.1007-000), filed on Mar. 16, 2001, the entireteachings of all of which are incorporated herein by this reference.This application is also related to and claims the benefit of earlierfiled U.S. Provisional Patent Application Ser. No. 60/556,328 entitled“Methods and Apparatus for Streaming Data in an Inductive CommunicationSystem,” (Attorney Docket No. 04-02p), filed on Mar. 25, 2004, theentire teachings of which are incorporated herein by this reference.

BACKGROUND

Inductive antenna devices have been incorporated in transceivers totransmit and receive wireless signals for quite some time. In a typicalapplication, a transceiver device supporting bi-directionalcommunication includes two specifically tuned antennas, one of which istuned for transmitting while the other is tuned for receiving.

Unlike RF (Radio Frequency) antennas, the transmit and receive paths forinductive antennas or transducer assemblies are often tunedindependently of each other for more efficiently transmitting andreceiving wireless signals. For example, inductive transducer assembliesused for transmitting respective inductive signals are generally tunedso they effectively have a low impedance. Conversely, inductivetransducer assemblies used for receiving are typically tuned so theyeffectively have a high impedance.

Conventional inductive systems supporting two-way communications includeseparate coils, one of which is pre-tuned for transmitting an inductivesignal and another of which is pre-tuned for receiving at a particularcarrier frequency.

SUMMARY

Recent advancements in integrated circuit technology render it possibleto reduce the overall size of wireless transceiver devices becausesemiconductor chips provide yet more and more functionality in smallerpackages. Additionally, the size and weight of power sources (e.g.,battery devices) for powering corresponding wireless devices has beenreduced to support increased portability. Thus, wireless transceiverdevices are now smaller than ever before.

Unfortunately, conventional inductive transceiver devices are not yetsmall enough. Users continue to demand smaller and smaller devices thatprovide the same or better quality of communication. As a result, therelative size and weight associated with the use of transducers andassociated conventional circuitry for transmitting and receiving can beprohibitive due to space restrictions in certain wireless applications.

It would be an advancement in the art to reduce the power, cost, sizeand weight of a transceiver system (e.g., an inductive communicationdevice) for transmitting and receiving wireless signals based on use ofan electronically tunable inductive communication system that reduces oreliminates a need for implementing redundant circuitry, overly complexcircuitry, or manually adjusting trim pots or other circuit components.

More specifically, embodiments of the present invention provide a noveland useful way of tuning transducer elements over conventional methods.For example, in one embodiment of the present invention, electroniccircuitry supports utilization of a pulse to tune a transducer (e.g., acoil that produces or receives a magnetic field) for transmitting orreceiving. In one embodiment, a control circuit generates a digitalpulse of variable width to produce a control voltage. This controlvoltage drives a varactor element whose capacitance changes depending onthe magnitude of the produced control voltage. The varactor elementforms part of a tank circuit. Consequently, the generation of a pulse ofvariable width controls an operating frequency of the tank circuit. Inone embodiment, the tank circuit includes an inductive element such as acoil that is tuned to produce or receive a magnetic or inductive field.Tuning the tank circuit and, more specifically, the coil by generating apulse of variable width provides flexibility because a simple,lightweight, and low cost CMOS logic circuit that generates pulses ofpredetermined widths can be used to tune the coil for transmitting orreceiving.

Now more generally, an embodiment of the present application includes atransducer assembly that supports transmission and/or reception ofinductive signals (e.g., wireless signals). A control circuit selects adesired operating frequency to tune the transducer assembly. The controlcircuit couples to or includes a pulse generator circuit. To tune thetransducer assembly, the control circuit initiates the pulse generatorcircuit to produce a pulse of a predetermined width in a control signalto tune the transducer assembly to the desired operating frequency.Thus, a control circuit generating a digital stream of information canbe used to dynamically or electronically tune a transducer assembly to adesired operating frequency for unidirectional or bidirectionalcommunications.

In one embodiment, the control circuit tunes a transducer in thetransducer assembly to transmit an inductive signal (e.g., a magneticfield) at a first carrier frequency based on initiation of the pulsegenerator circuit to generate a first pulse of variable width. Followingtransmission of an inductive signal from the transducer on the firstcarrier frequency, the control circuit re-tunes the transducer in thetransducer assembly to receive an inductive signal on a second carrierfrequency based on initiation by the control circuit to generate a pulseof variable width.

As discussed above and according to one embodiment, generation of apulse of a particular width by the pulse generator causes a controlvoltage generator to produce a control voltage that tunes a transducersuch as an inductive coil in the transducer assembly by means of avoltage controlled capacitor (varactor). The control voltage generatorproduces larger control voltages for longer pulse widths received fromthe pulse generator circuit. Consequently, a short pulse width producesa lower voltage while longer pulse widths produce larger control voltagevalues.

In one embodiment, the control voltage drives a circuit element whoseimpedance changes depending on an applied voltage. The circuit elementcan be, for example, a capacitive circuit element such as a varactorelement whose capacitance is set based on the applied control or controlvoltage. In such an embodiment, the varactor forms part of a tankcircuit whose operating frequency is set depending on the appliedcontrol voltage. Thus, the tank circuit, potentially including atransducer coil to transmit or receive a magnetic field, can be tuneddepending on the applied control voltage. A typical application of theembodiments discussed herein involves first tuning the transducerassembly and, thereafter, transmitting or receiving an inductive field.

According to further embodiments, the control circuit includes a resetsignal to reset the control voltage generator. Consequently, the controlcircuit can initially generate the control signal to set the controlvoltage and tune the transducer assembly to a desired operatingfrequency. After transmitting or receiving data on the transducerassembly, the control circuit can reset the control voltage tosubstantially zero volts. The control circuit then initiates thegeneration of another pulse of a given width to produce another controlvoltage to tune the transducer assembly to another desired operatingfrequency. Accordingly, the control circuit can initiate setting thetransducer to different desired operating frequencies.

In one embodiment, the control circuit initiates generation of a pulse(e.g., a square wave) in the control signal to produce a control voltageand tune the transducer tank circuit to a first carrier frequency.Thereafter, the control circuit initiates generation of a reset signalto reset the control voltage prior to later re-tuning (e.g., viageneration of another pulse) the transducer tank circuit of thetransducer assembly to a different carrier frequency.

According to yet a further embodiment, the transducer assembly includesmultiple transducer circuits, each of which includes one or moretransducers (e.g., coils) to transmit and/or receive magnetic fieldsignals. The control circuit, in addition to initiating generation ofthe pulses to generate control voltages, selects a given transducercircuit of multiple transducer circuits in the transducer assembly fortuning. For example, the control circuit generates a series of pulses ofvariable widths at different times (for a digital stream of high and lowvoltage states) to generate control voltages that, over time, tune eachof the selected transducer circuits to a desired operational frequency.Additionally, in one embodiment, the control circuit activates a singletuned transducer circuit in the transducer assembly for transmissionand/or reception of inductive signals.

In one embodiment, the control circuit includes associated memory tostore calibration information including different pulse widths to beapplied to the control voltage generator for tuning a transducer circuitin the transducer assembly to respective different operatingfrequencies. For example, the control circuit accesses the calibrationinformation in memory to identify the duration of pulses required totune the transducer assembly to the desired operating frequency.

The memory can store different calibration tables for respectivelytuning the transducer assembly depending on whether the control circuitsets the transducer assembly for transmitting or receiving. This isbecause a control voltage for setting the transducer assembly to adesired operating frequency for transmitting and receiving may not bethe same. For example, when in a transmit mode, the control circuitinitiates generation of the control voltage to a given value to set thetransducer assembly to a first desired operating frequency fortransmitting. However, switching the transducer assembly to a receivemode and applying the same control voltage may result in tuning thetransducer to receive at an operating frequency different the firstoperating frequency due to a difference of parasitic impedances in thetransducer assembly which vary depending on whether it is set to atransmit mode versus a receive mode. Thus, according to one embodiment,to receive and transmit at the same operating frequency, the controlcircuit must generate two different pulse widths to produce twodifferent respective control voltages so that the same transducer (e.g.,wire coil) in the transducer assembly can both transmit and receive atthe same operating frequency.

Accordingly, one embodiment of the transducer assembly discussed aboveincludes a tank circuit whose parasitic impedances change depending onwhether the transducer assembly is set to a transmit mode versus areceive mode. As previously discussed, the tank circuit can include arespective inductive element supporting transmission and/or reception ofinductive signals.

Use of the pulses to reconfigure a transducer assembly to a desiredoperating frequency for transmitting and receiving requires fewercircuit components than conventional applications. For example,conventional methods employ two separate inductive coils, one tuned fortransmitting and another tuned for receiving. This requires excesscircuit board space and adds unnecessary weight to the transducerassembly. Use of techniques discussed herein enable transmission andreception on the same transducer without a significant delay betweensetting a corresponding operational mode of the transducer assembly.

According to one embodiment, the control circuit maintains calibrationinformation based on prior test circuit measurements. For example, in atest mode, the control circuit tunes the transducer assembly through arange of settings via application of pulses of different widths whilereceiving a known test magnetic field signal. Based on which appliedpulse width (or setting) produces a strongest received signal for thereceived test magnetic field, the control circuit stores this derivedcalibration information in memory for later use. A similar calibrationroutine can be used to calibrate the transducer assembly fortransmitting. For example, the transducer assembly can be tuned based onapplying a range of pulse widths to identify settings of the transducerassembly for a transmit mode. Consequently, based on the abovecalibration testing, the control circuit associated with the transducerassembly can identify respective operating frequencies of a transducercircuit in the transducer assembly for the different applied pulsewidths.

Embodiments of the invention are well-suited for use in shorter-rangewireless applications such as those that support inductive or magneticcoupling, but the broader general concepts discussed herein can beextended to other applications as well.

Other embodiments of the invention include a processor device (e.g., thecontrol circuit) configured to support the aforementioned methodoperations disclosed herein as embodiments of the invention to configurea transducer assembly. In such embodiments, the processing device has anassociated memory system and an interconnect. The interconnect supportscommunications between the processor and the memory system. The memorysystem is encoded with a control management application that, whenexecuted on the processor device, produces a control process. Thecontrol process initiates tuning and re-tuning of the transducerassembly and corresponding one or multiple transducers for transceiving(e.g., transmitting or receiving) magnetic fields.

Yet other embodiments of the invention disclosed herein include softwareprograms to perform the method embodiment and operations summarizedabove and disclosed in detail under the heading Detailed Descriptionbelow. More particularly, certain embodiments of the invention include acomputer program product (e.g., a computer-readable medium) includingcomputer program logic encoded thereon that may be executed on aprocessor device to perform the operations (e.g., the methods) asdiscussed herein. Thus, embodiments of the invention include software orcomputer code. Other arrangements of the invention include hardware suchas analog/digital circuit devices to perform the techniques discussedherein.

One embodiment of the invention is directed to a computer programproduct that includes a computer readable medium having instructionsstored thereon for supporting tuning of a transducer assembly. Theinstructions, when carried out by a processor, enable the processor toperform the steps of: i) identifying a desired operating frequency and aspecific transducer to tune in the transducer assembly, ii) initiatinggeneration of a pulse in a control signal to tune the selectedtransducer in the transducer assembly to the desired operatingfrequency, and iii) utilizing the tuned transducer in the transducerassembly for at least one of transmission and reception of inductivesignals.

Yet another embodiment of the invention is directed to a technique of:i) coupling one of multiple transducers to a circuit to transmit orreceive a magnetic field; ii) selecting a frequency for communicatingvia the magnetic field; iii) via use of a varactor device, sweepingthrough a range of impedance values to identify which of multiple valuesis optimal for transmitting or receiving over the coupled one ofmultiple transducers at the selected frequency; and iv) storing anidentified optimal impedance value for later use.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of embodiments of the invention, as illustrated in theaccompanying drawings and figures in which like reference charactersrefer to the same parts throughout the different views. The drawings arenot necessarily to scale, emphasis instead being placed uponillustrating the embodiments, principles and concepts of the invention.

FIG. 1 is a diagram illustrating a technique of tuning a transducerassembly according to an embodiment of the invention.

FIG. 2 is a schematic diagram of a tuning circuit according to anembodiment of the invention.

FIG. 3 is a timing diagram illustrating signals for tuning according toan embodiment of the invention.

FIG. 4 is a flowchart illustrating a technique according to anembodiment of the invention.

DETAILED DESCRIPTION

In one embodiment of the invention, electronic circuitry supportsutilization of pulses to tune a transducer assembly (e.g., one or morecoils that produce or receive a magnetic field) for transmitting orreceiving. For example, an embodiment of the invention includesgenerating pulses of different widths to produce different controlvoltages. A produced control voltage drives a variable capacitor (e.g.,a varactor element) whose capacitance changes depending on a magnitudeof the produced control voltage. The variable capacitor forms part of atank circuit. Consequently, the pulse of variable width controls anoperating frequency of the tank circuit. Further, the tank circuitincludes a transducer such as an inductive coil that is tuned totransmit or receive a magnetic or inductive field. Tuning the tankcircuit and, more specifically, the coil by generating a pulse ofvariable width enables fast electronic tuning via a simple electroniccircuit that generates the pulses.

FIG. 1 is a block diagram of a communication system 100 includingcircuitry for tuning a transducer assembly 150 according to anembodiment of the invention. As shown, communication system 100 includescontrol circuit 110 (e.g., a processor device), correspondingcalibration information 120 (e.g., stored in memory), pulse generatorcircuit 125, control voltage generator 140, and transducer assembly 150.Pulse generator circuit 125 produces a control signal 130 and resetsignal 132 as initiated by control circuit 110. Based on the controlsignal 130 and reset signal 132, control voltage generator 140 producesa control voltage 145 applied to transducer circuits 160-1, 160-2, and160-3. Each transducer circuit 160 includes a respective capacitiveelement 170 such as a varactor device whose capacitance changesdepending on applied control voltage 145. Additionally, each transducercircuit includes a respective transducer 180 such as a coil fortransmitting and/or receiving inductive signals.

Note that transducer assembly 150 can include one or more transducercircuits 160 (and respective transducers 180 such as inductive coilsthat transmit and receive magnetic fields) depending on the application.Also, in one embodiment, transducers 180-1, 180-2, and 180-3 arepositioned in different orientations such as on respective a X-axis,Y-axis, and Z-axis for transmitting and receiving inductive signals fromdifferent angles. In one embodiment, transducer assembly 150 isoptionally portable so that its orientation is not fixed with respect toa target transceiver with which it communicates. Use of transducers oneach of an X, Y and Z axis ensures that transducer assembly 150 maycommunicate with another inductive transceiver device having as few as asingle transducer coil to communicate. Additional details concerningcommunication techniques and possible circuit configurations can befound co-pending U.S. patent application Ser. No. 10/004,989 filed onDec. 3, 2001, entitled “Wireless Communications Over a TransducerDevice,” the entire teachings of which are incorporated herein by thisreference.

In one embodiment, a respective capacitive element 170 and transducer180 form part of a tank circuit (e.g., LC circuit) in a transducercircuit 160. Application of the control voltage 145 tunes the tankcircuit and, more particularly, a respective transducer 180 fortransmitting or receiving magnetic field signals (a.k.a., inductivesignals).

As discussed above, embodiments of the present invention provide a noveland useful way of tuning transducers 180 for transmitting or receivingdata from a remote device over a wireless link. For example, electroniccircuitry supports utilization of a of a pulse to tune a transducer 180(e.g., a coil that produces or receives a magnetic field) fortransmitting or receiving. More specifically, an embodiment of theinvention includes generating a duration 139 of a pulse 137 to produce acontrol voltage 145. In one embodiment, an example pulse has a width of25 microseconds and repeating once every 10 milleseconds. The pulsewidth and repetition rate can change depending on the application. Inone embodiment, operating frequencies of the transducers range from 10to 15 MHz.

Another aspect of the present invention concerns selecting of componentsdisposed in either the transmit or receive circuit. Although anycomponent values generally can be selected for use in communicationsystem 100, component values are typically selected to provide a desiredperformance. In space-restricted applications, an actual size ofcomponents is a factor to consider for selecting component values.Typically, capacitor values are on the order of nanofarads orpicofarads. In other applications, power dissipation and signalbandwidth are factors to consider for properly selecting componentvalues. Thus, selection of components can differ depending on aparticular application.

Although 13 MHz is a typical operating frequency for transmitting and/orreceiving in one application, a selected carrier frequency can be anysuitable setting such as between 0.5 and 60 MHz or even outside thisrange.

One application of the invention relates to changing the operatingfrequency of the transducer assembly 150. In the event that otherwireless devices are utilizing a similar carrier frequency as transducerassembly 150, interference typically can be avoided during operationaluse in the field by dynamically tuning a transmitter/receiver of thetransducer assembly 150 to transmit and receive at another carrierfrequency.

The control voltage 145 generated by control voltage generator 140provides a bias to capacitive elements 170 such as varactor deviceswhose capacitance changes depending on a magnitude of the controlvoltage 145. The capacitive elements 170 form part of a respectivetransducer circuit 160 (e.g., a tank circuit) in transducer assembly150. Consequently, the generation of a pulse width 139 controls anoperating frequency of the transducer circuit 160.

In one embodiment, each transducer circuit 160 includes a respectivetransducer 180 such as a coil that is tuned to produce or receive amagnetic or inductive field.

Tuning the transducer circuit 160 and, more specifically, the transducer180 by generating a duration 139 of a pulse 137 provides flexibilitybecause a simple control circuit 110 or pulse generator circuit 125 thatgenerates a pulse or series of pulses over time can be used to tune thecoil for transmitting or receiving. For example, a control circuit 110or pulse generator circuit 125 generating a digital stream ofinformation (e.g., logic ones and zeros) can be used to dynamically orelectronically tune a transducer 180 in transducer assembly 150 to adesired operating frequency for unidirectional or bidirectionalcommunications. A simple pair of logic signals from the control circuit110 is easily achievable using two pins on a standard CMOS ApplicationSpecific Integrated Circuit (ASIC). It would be quite difficult togenerate the control voltage directly on the ASIC since voltagesexceeding 30 volts may be required. This is typically not practicalusing standard CMOS integrated circuit processes.

As discussed, transducers 180 can be inductive devices for generating awireless signal such as a magnetic field. In such an application,transducer 180 can be a coiled strand of wire. A magnetic field can begenerated when a current is driven through the coiled wire. A ferriterod can be disposed at a core of the coiled strand of wire to enhancedirectional or signal strength characteristics of transducer 180 forreceiving and transmitting a magnetic field. In a specific application,transducer 113 includes a 4×8 mm (millimeters) ferrite rod having fourturns of wire. However, specific attributes of transducers 180 can varydepending on a particular application.

In one application, the control circuit 110 and pulse generator circuit125 are part of a CMOS-based ASIC device that operates at under 3 voltsDC. Tuning of the transducer circuits 160 may require higher voltagessuch as 30 volts DC or higher. In such an application, pulse generatorcircuit 125 produces a stream of digital pulse widths 137 between 0 and3 volts. Depending on a duration 139 of the pulse within the stream 137,control voltage generator 140 provides a step-up voltage function to arange between 0 and 30 volts DC or even higher. Accordingly, a lowvoltage device such as control circuit 110 running on 3 volts caninitiate generation of a control voltage 145 much larger than 3 voltssuch as up to 30 volts or higher. No external high voltage power supplyis required.

Control circuit 110 also generates mode selection signals 192 toconfigure transducer assembly 150. For example, in one embodiment,control circuit 110 chooses which of multiple transducers 180 on whichto transmit or receive inductive signals. Control circuit 110 also canset transducer assembly 150 to a transmit mode and a receive mode.Control circuit 110 transmits or receives modulated signals via signal195.

In one embodiment, the control circuit 110 tunes a selected transducer180 (such as transducer 180-1) in the transducer assembly 150 totransmit or receive an inductive signal (e.g., a magnetic field) at afirst carrier frequency based on initiation of the pulse generatorcircuit 125 to generate a first duration 139 of pulse 137. Followingtransmission of an inductive signal from the transducer 180 on the firstcarrier frequency, the control circuit 110 resets the control voltage145 via reset signal 132 and re-tunes the transducer 180 in thetransducer assembly 150 to receive or transmit an inductive signal on asecond carrier frequency based on initiation by the control circuit 110causing the control voltage generator 140 to generate a second duration139 of pulse 137. A time required to electronically tune the transducerassembly 150 can range between 5 to 25 microseconds. In this way,transducer assembly 150 easily supports changing of communication modesin a short period of time.

As discussed above and according to one embodiment, generation of thepulse 137 by the pulse generator circuit 125 causes control voltagegenerator 140 to produce a control voltage 145 that tunes a transducer180 in the transducer assembly 150. The control voltage generator 140produces larger control voltages 145 for longer durations of pulsesreceived from the pulse generator circuit 125. Consequently, a shortduration 139 of pulse 137 produces a lower control voltage 145.

According to further embodiments, and as briefly discussed, the controlcircuit 110 includes a reset signal 132 to reset the control voltage 145to zero to reset tuning of the transducer assembly 150. Consequently,the control circuit 110 can initially generate the control signal 130 toset the control voltage 145 and tune the transducer assembly 150 to adesired operating frequency. After the transmitting or receiving data onthe transducer assembly 150, the control circuit 110 resets the controlvoltage 145 to substantially zero volts. Following a reset of thecontrol voltage 145, the control circuit 110 can again initiategeneration of another pulse of different pulse width 137 to produce acontrol voltage 145 to tune the transducer assembly 150 to anotherdesired operating frequency. Accordingly, the control circuit 110 caninitiate setting the transducer assembly 150 to different desiredoperating frequencies.

In one embodiment, the control circuit 110 initiates generation a pulse137 in the control signal 130 to produce a control voltage 145 and tunea respective transducer circuit 180 (e.g., one of transducer circuit180-1, transducer circuit 180-2, and transducer circuit 180-3) to afirst carrier frequency and, thereafter, the control circuit 110initiates generation of a reset signal 132 to reset the control voltage145 prior to later re-tuning (e.g., via generation of another duration139 of pulse 137) the transducer circuit 180 of the transducer assembly150 to a different carrier frequency.

Although FIG. 1 illustrates multiple transducer circuits 160 andrespective transducers 180, in one embodiment the transducer assembly150 includes only a single transducer circuit 160 for tuning andtransmission and/or reception of inductive signals.

In one embodiment, the control circuit 110 includes associated memory tostore calibration information 120 including different pulse widths to beapplied to the control voltage generator 140 for tuning a transducercircuit 180 in the transducer assembly to respective different operatingfrequencies. For example, after identifying a desired operatingfrequency for tuning the transducer assembly 150 and transmitting orreceiving data, the control circuit 110 accesses the calibrationinformation 120 in memory to identify the duration 139 of pulse 137required to tune the transducer assembly 150 to the desired operatingfrequency.

Memory (e.g., on-chip or off-chip memory) associated with the controlcircuit 110 can store different calibration tables for respectivelytuning the transducer assembly 150 depending on whether the controlcircuit 110 sets the transducer assembly 150 for transmitting orreceiving. This is because a control voltage 145 for setting thetransducer assembly 150 to a desired operating frequency for a transmitmode may not be the same as for a receive mode. For example, when in atransmit mode, setting the control voltage 145 to a given value sets thetransducer assembly 150 to a first desired operating frequency fortransmitting. However, switching the transducer assembly 150 to areceive mode and applying the same control voltage 145 to a respectivetransducer circuit 160 may result in tuning a given transducer toreceive at an operating frequency different the first operatingfrequency due to a difference of parasitic impedances in the transducercircuit 160. That is, the parasitic impedances associated with atransmit mode and a receive mode of the transducer assembly 150 aredifferent although the same control voltage 145 is used for tuning bothcircuits. Thus, according to one embodiment, to receive and transmit atthe same operating frequency, the control circuit 110 generates twodifferent sets of pulse durations 139 to produce respective controlvoltages 145 (at different times) so that the same transducer 180 in thetransducer assembly 150 can both transmit and receive at the sameoperating frequency but for different cycles.

Accordingly, one embodiment of the transducer assembly 150 discussedabove includes a tank circuit (e.g., transducer circuit 160) whoseparasitic impedances change depending on whether a respective transducer180 is set to a transmit mode versus a receive mode. Use of techniquesdiscussed herein enable transmission and reception on the sametransducer 180 without a significant delay between setting correspondingoperational modes of the transducer 180.

According to one embodiment, the control circuit 110 maintainscalibration information based on prior test measurements. For example,in a test mode, the control circuit 110 can tune the transducer assembly150 (more specifically, each of transducers 180) through a range oftunings via application of different durations of pulse 137 whilereceiving a known test magnetic field signal from a test circuit withinrange of transducer assembly 150. Based on which applied pulse duration(or tuning) produces a strongest received signal for the received testmagnetic field, the control circuit 110 stores this derived calibrationinformation 120 in memory for later use.

A similar calibration routine can be used to calibrate the transducerassembly 150 for transmitting. In other words, the transducer assembly150 can be tuned based on applying a range of different pulse durationswhile in a transmit mode. Test receiver equipment can be used to measurean inductive field signal generated by the transducer assembly 150 toidentify an operating frequency of the transducer assembly 150 for thedifferent tunings. Associated calibration information derived from thetest is stored as calibration information 120. Consequently, based onthe above calibration testing, the control circuit 110 associated withthe transducer assembly 150 can identify respective operatingfrequencies of each respective transducer circuit 160 in the transducer150 assembly for the different applied pulse durations and respectivecontrol voltage values.

In another embodiment, calibration of the transducer assembly 150 cantake place in the field during usage of the devices for magneticcommunications. For example, while a magnetic communication device A(e.g., an MP3 player) is transmitting to a magnetic communication deviceB (e.g., wireless headphones) under a static set of operating conditions(i.e., the devices are not moving relative to each other or movement isaveraged over a long measurement period, thus making the magnetic fieldat the receiver constant), device B may tune its receiver viaapplication of different durations of pulse 137 and determining if thecurrent pulse width 139 should be changed to a new pulse width 139 inorder to maximize the received signal. In a similar manner, device A'stransmitter may be tuned in the field by having device B measure thereceived signal for different pulse widths 139 of device A and, bycommunicating with device A to determine the pulse width 139 in device Awhich results in the strongest transmitted signal at a selectedfrequency. In this manner, devices in the field can be “self-tuning” toadjust to changes in environmental conditions, component values withinthe devices, differences in operating frequencies between devices, andother such system operating conditions. Self tuning is also described inearlier filed U.S. patent application Ser. No. 10/004,989 entitled“Wireless Communication Over a Transducer Device,” filed on Dec. 3,2001, which has been incorporated herein by reference. FIG. 2 is acircuit diagram illustrating an electronically tunable communicationsystem 200 according to an embodiment of the invention. As shown,communication system 200 includes a control circuit 210, a controlvoltage generator 240, and respective transducer circuits 260-1, 260-2,and 260-3.

In the example embodiment shown, control voltage generator 240 is a highvoltage pulse circuit that provides a control voltage 203 (e.g., tuningvoltage) which is applied to tune varactors 270-1, 270-2, and 270-3. Inone embodiment, the transducer circuits 280 are driven by differentialdrivers 241, 242, and 243 such as those in a CMOS mixed signaltransceiver circuit in control circuit 210, which also generates amodulated signal to be applied to each of the drivers 241, 242, and 243to produce a modulated magnetic field. Control circuit 210 deliversmaximum power to produce a respective modulated magnetic field signalwhen using differential type drivers 241, 242, and 243, although singleended type drivers may also be used.

CMOS circuits typically have input/output signal specifications lessthan 5 volts. In general, use of more advanced and fine line widthprocesses during fabrication of the circuits results in a lower circuitoperating voltage. Certain CMOS devices run off 3 volts or less voltagesources. In contrast, varactors 270 generally require higher voltagesfor tuning, such as up to 30 volts for a Sanyo™ VC383 as shown. Anadvantage of using a high voltage pulse circuit (e.g., control voltagegenerator 240) is that the pulse circuit including inductor 207 cangenerate a voltage higher than the output voltage of a CMOS mixed signaltransceiver such as control circuit 210 without the use of an externalhigh voltage power supply.

Another advantage of communications system 200 is that a simple circuit(e.g., control voltage generator 240) under control of a CMOS mixedsignal transceiver control circuit 210 can initiate generation ofcontrol voltage 203 (or, as previously discussed, control voltage 145).

The control voltage 203 drives each of the three varactors 270-1, 270-2,and 270-3. Thus, multiple transducer circuits 260 share use of the samecontrol voltage 203. Note that other embodiments of communication system200 can include a separate control voltage generator 240 for each of thetransducer circuits 280 rather than a single control voltage generatorthat is shared.

Since the pulse width of the CHARGE signal 201 determines the applied DCcontrol voltage 203 to the varactors 270-1, 270-2, 270-3 as discussedabove (i.e., the control voltage 203 applied to the varactors determinesthe capacitance of the varactors), storing the digital representation ofthe pulse width in control circuit 210 enables the control circuit totune each transducer 280-1, 280-2, and 280-3. Furthermore, differentpulse widths values for each of the different transducers 280 (in eitherreceive or transmit mode) and corresponding operating frequencies can bestored in the control circuit 210. In one embodiment, a pulse width“table” associated with control circuit 210 provides a tuning map fordifferent operating conditions. Such a table may further includeadjustment information that allows tuning and compensation to beperformed in real-time in the field during use of the communicationsystem 200. For example, six values may be stored for a three transducersystem, three settings for each transducer during a transmit mode andthree settings for each transducer when switched to a receive mode.Additional information may be stored to compensate for temperaturevariations, different transmit frequencies, different receivefrequencies, and other such settings depending on environmental oroperational conditions.

The operation of communication system 200 is as follows. Tuning occursby applying a control voltage 203 through the 27 K resistors 252, 262and 272 to bias the varactors 270-1, 270-2, and 270-3 respectively. Inone embodiment, only one transducer 280 is activated at a time bycontrol circuit 210, which selects the appropriate transceiver driver241, 242, and 243 on which to drive a modulated signal for transmissionover a respective transducer 280 as a magnetic field signal. Controlcircuit 210 selects different operational modes (e.g., which transducer280 on which to receive a magnetic field) via setting of switch 244. Forexample, receiver 245 receives a modulated signal depending on a settingof switch 244.

In one embodiment, a magnitude of the control voltage 203 generated bythe control voltage generator 240 is greater than a voltage magnitude ofthe pulse 137 in the CHARGE signal 201 received from the pulse generatorcircuit 125 (or control circuit 210). For example, the voltage magnitudeof the pulse can be 3 volts (for a logic high portion of the pulse 137)while the magnitude of the control voltage 203 is up to 30 volts ormore. Thus, in one embodiment as in FIG. 1, the voltage magnitude of thepulse 137 generated by the pulse generator circuit 125 is less than 4volts and the magnitude of the control voltage 145 is greater than 6volts.

FIG. 3 is a timing diagram for operating communication system 200according to an embodiment of the present invention. As shown, timingdiagram illustrates a data signal 310, a reset signal 202, a chargesignal 201 (e.g., a control signal), and a control voltage 203.

Prior to transmission of data during a time slot (e.g., during the firstshown GUARD period), control circuit 210 generates reset signal 202 totemporarily activate transistor 206 and reset control voltage 203 oncapacitor 204 to zero volts. Thereafter, control circuit 210 generates aCHARGE signal 201 (e.g., a pulse of WIDTH 1) and the reset signal 202 isdeactivated to enable charge to accumulate on capacitor 204. Applicationof the CHARGE signal 201 to inductor 207 and deactivation of the resetsignal 202 results in producing a control voltage 203 to a predeterminedvoltage value as determined by the duration of the applied pulse (e.g.,WIDTH 1). Thus, when the reset signal 202 is active, transistor 206turns on causing current to flow through inductor 207. While a chargesignal 201 is still applied, control circuit 210 opens transistor 206 bysetting reset signal 202 low again. Current continues to flow throughinductor 207, charging control voltage 203 to an appropriate voltage(which can be up to 30 or more volts). As discussed, application of thecontrol voltage 203 to the varactors 270 tunes one of the respectivetransducers 280 for transmitting or receiving data.

In one embodiment, the control circuit 210 varies the leading edge(e.g., rising edge) of the CHARGE signal 201 relative to thecorresponding falling edge to change a value of generated controlvoltage 203. For example, applying a logic high voltage on charge signal201 for a longer duration (e.g., WIDTH 2 is greater than WIDTH 1) whiletransistor 206 is active results in more current flowing throughinductor 207. When switching the transistor 206 off, a greater controlvoltage 203 is produced for WIDTH 2 due to the higher current throughinductor 207 for this case. In other embodiments, the falling edge ofthe CHARGE signal 201 is adjusted to impact a value of the controlvoltage 203. Also, the rising and falling edges of the RESET signal 202can be adjusted to vary a value of the control voltage 203.

After applying the CHARGE signal 201 to generate the control voltage 203to a voltage V1, control circuit 210 initiates transmitting data from arespectively tuned transducer 280 during TRANSMIT DATA period. Diode 208prevents energy in capacitor 204 from leaking back through the controlcircuit 210. In other words, the control voltage remains constant duringthe TRANSMIT DATA period. Control circuit 210 excites a tuned transducer280 by applying a modulated signal via respective one or more outputdrivers 241, 242 or 243.

After transmitting data during a TRANSMIT DATA cycle, control circuit210 generates a RESET pulse 202 and thereafter applies a different pulsewidth (e.g., WIDTH 2) in the CHARGE signal 201 to generate a controlvoltage 203 of V2 to tune a transducer for receiving data during RECEIVEDATA cycle.

Referring again to FIG. 2, control circuit 210 performs selection of atransducer 280 for receiving based on use of the three-to-one T/R switch244. In one embodiment, and as discussed above, a different pulse widthis used to tune a selected transducer 280 depending on whether it is setto a transmit or receive mode. This is because parasitics of the circuitchange depending a setting of the drivers 241, 242, and 243 and the T/R(transmit/receive) switch 244. Thus, an advantage of communicationsystem 200 is that such a circuit topology easily compensates forparasitic circuit differences.

The predetermined pulse widths of CHARGE signal 201 can be calculatedduring a calibration or tuning cycle as discussed. The method involvesselecting a transducer 280, its operating mode (transmit or receive),and its operating frequency. Through an iterative process, an on-chipmicroprocessor associated with the control circuit 210 generates aseries of increasingly longer pulse widths that are applied to thecontrol voltage generator 240 via application of the CHARGE signal 201.A separate circuit from the transducer assembly 150 generates a testmagnetic field signal at a given operating frequency. The transducerassembly 150 receives the test magnetic field on one or more transducers280. The control circuit 210 measures a feedback portion of this testmagnetic field signal that effectively represents the tuning state ofthe transducer. The pulse width that results in the largest fed backtest signal is retained in memory as the tuning value for thatparticular test setting.

Control circuit 210 can generate a tuning table by repeating this methodfor different transducers, modes and environmental conditions, andoperating frequencies. During normal operation values from this tableare accessed and implemented to dynamically tune the communicationsystem 200 under varying operating conditions.

In one application, transducer assembly operates in a TDD (Time DivisionDuplex) system that can be configured to alternately transmit andreceive in synchronization with a base transceiver unit. During atransmit frame, driver 241, 242, and 243 are selectively activated (tocontrol power output levels) and to apply a GMSK modulated square waveto transducers 280 and related circuitry.

In view of the above-mentioned embodiments, FIG. 4 is a flowchart 400illustrating a technique of electronically tuning a transducer accordingto an embodiment of the invention.

In step 410, the control circuit 110 identifies a desired operatingfrequency, mode, and transducer to tune in the transducer assembly 150.

In step 420, the control circuit 110 initiates generation of an activecontrol signal (e.g., a charge phase or a time in which application ofthe control signal causes a change to a produced control voltage 145)for a specified duration 139 of time to tune the transducer assembly 150to the desired operating frequency. Different durations of generatingthe active control result in different respective tunings of thetransducer assembly 150 as previously discussed.

In step 430, the control circuit 110 utilizes the tuned transducerassembly for at least one of transmission and reception of inductivesignals. For example, in a transmit mode, the control circuit 110modulates a data signal onto a carrier frequency to which the transducerassembly 150 is tuned. In a receive mode, the control circuit 110receives a modulated data signal based on a carrier frequency to whichthe transducer assembly 150 is tuned.

Embodiments of the invention are well-suited for use in shorter-rangewireless applications such as those that support inductive or magneticcoupling, but the broader general concepts discussed herein can beextended to other applications as well. For example, the technique ofgenerating pulses can be used to adjust attributes of other types ofelectronic circuitry.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims. As such, the foregoingdescription of embodiments of the invention is not intended to belimiting.

1. A method of electronically tuning a transducer assembly, the methodcomprising: generating a first control signal for a respective firstduration of time to tune the transducer assembly to a first operatingfrequency; and utilizing the transducer assembly tuned to the firstoperating frequency for at least one of transmission and reception ofinductive signals.
 2. A method as in claim 1 further comprising:following use of the transducer assembly at the first operatingfrequency: generating a second control signal for a respective secondduration of time to tune the transducer assembly to a second operatingfrequency; and utilizing the transducer assembly tuned to the secondoperating frequency for at least one of transmission and reception ofinductive signals.
 3. A method as in claim 1 further comprising:selecting a given transducer circuit of multiple transducer circuits inthe transducer assembly for tuning to the first operating frequency, thegiven transducer circuit including a respective transducer on which toat least one of receive and transmit the inductive signals; and whereingenerating the first control signal includes generating the firstcontrol signal to include a pulse whose duration at least in partdetermines tuning of the given transducer circuit.
 4. A method as inclaim 3, wherein tuning the given transducer circuit includes: utilizingthe pulse in the first control signal to generate a respective controlvoltage; and applying the respective control voltage to a circuitcomponent of the given transducer circuit to tune the respectivetransducer to the first operating frequency, an impedance of the circuitcomponent and respective tuning of the given transducer circuit changingdepending on a magnitude of the respective control voltage applied tothe circuit component.
 5. A method as in claim 3, wherein generating thepulse in the control signal produces a control voltage that tunes thegiven transducer circuit in the transducer assembly to operate at thefirst operating frequency, a magnitude of the control voltage beinggreater than a respective voltage amplitude associated with the pulse inthe control signal.
 6. A method as in claim 1 further comprising:storing calibration information for tuning a transducer in thetransducer assembly to the first operating frequency, which is selectedfrom a set of multiple different possible operating frequencies; andutilizing the calibration information to identify attributes of arespective control signal required to tune the transducer assembly tothe first operating frequency.
 7. A method as in claim 1 furthercomprising: selecting the first operating frequency to avoidinterference with other wireless devices.
 8. A method as in claim 2further comprising: selecting the first operating frequency and thesecond operating frequency to avoid interference with other wirelessdevices.
 9. An apparatus comprising: a transducer assembly including atleast one transducer that supports at least one of transmission andreception of inductive signals; a control circuit that generates a firstcontrol signal at a first voltage level; a voltage generator circuitthat generates, based on characteristics of the first control signal, asecond control signal at a second voltage level for tuning thetransducer assembly to a desired operating frequency.
 10. An apparatusas in claim 9, wherein a respective voltage amplitude of the secondcontrol signal is greater than a respective voltage amplitude of thefirst control signal.
 11. An apparatus as in claim 9, wherein arespective voltage amplitude of the second control signal is greaterthan a supply voltage used to power the control circuit, which isfabricated using CMOS technology.
 12. An apparatus as in claim 9,wherein the first control signal includes at least two successivepulses.
 13. An apparatus as in claim 9, wherein the transducer assemblyincludes multiple transducer circuits, the control circuit selecting agiven transducer circuit of multiple transducer circuits in thetransducer assembly for tuning, the given transducer circuit including arespective transducer element on which to at least one of receive andtransmit the inductive signals.
 14. An apparatus as in claim 9, whereinthe voltage generator circuit applies the second control signal to acapacitive circuit component of the transducer assembly to tune arespective transducer in the transducer assembly to the desiredoperating frequency, an impedance of the capacitive circuit componentchanging depending on a voltage magnitude of the second control signal.15. An apparatus as in claim 14, wherein the capacitive circuitcomponent is a varactor device whose impedance varies depending on amagnitude of the second control signal, the impedance of the capacitivecircuit component being used to tune the respective transducer to thedesired operating frequency.
 16. An apparatus as in claim 13, whereinthe control circuit has access to calibration information indicatingrespective values associated with the first control signal for tuningthe respective transducer element in the given transducer circuit todifferent operating frequencies, the control circuit accessing thecalibration information to identify a respective setting of the firstcontrol signal to be used to tune the respective transducer element inthe given transducer circuit to the desired operating frequency.
 17. Amethod comprising steps of: enabling a transducer element in arespective transducer assembly to receive a magnetic field; generatingmultiple different control signals to vary an impedance of a varactordevice and tune the transducer element to receive on differentrespective operating frequencies; identifying which of the multipledifferent control signals is optimal for receiving the magnetic field;and storing an identified optimal control signal value for later use.18. A method as in claim 17, wherein the multiple different controlsignals include pulses and a respective duration of the pulses tunes thetransducer element for receiving the magnetic field.